남극대구의 Type II 결빙방지단백질

Abstract

Organisms living in the cold environment can survive subzero temperature by producing antifreeze proteins (AFPs) or antifreeze glycoproteins. An Antarctic cod, Notothenia corriceps which is one of the dominant fish in the Antarctic shallow water is known to contain the type I AFP gene. In the present study, we have identified two putative genes of another type of AFP, type II AFP, from the Antarctic cod by analysis of liver ESTs. Open reading frames of the two genes consist of 519 nucleotides encoding 172 amino acids (19.4 kDa) and are 68% identical with each other. These two putative AFPs show low level of amino acid identity with other type II AFPs known from longsnout poacher (B. rostratus, 39%), sea raven (H. americanus, 37%), rainbow smelt (O. mordax, 36.8%), Japanese smelt (H. nipponensis, 40.4%) and Atlantic herring (C. harengus, 39%). Although they seems to be type II AFPs, they have four disulfide-bonds unlike other type II AFPs which have five disulfide-bonds. When the protein sequences are projected onto the 3D structure of the sea raven AFP, residues on the surface of the globular structure are almost all hydrophilic: ~100% in sea raven and ~93% in N. corriceps. These hydrophilic residues might be important players in function of AFPs, preventing the ice crystal from growing by adhering to its surface. The cod AFPs are expressed as soluble recombinant proteins in E. coli and their ice binding characteristics are being under investigation.